1. Field of the Invention
The present invention relates to a substrate inspection apparatus, a substrate inspection method and a semiconductor device manufacturing method.
2. Related Background Art
Techniques using an electron beam have been used in defect inspections of semiconductor patterns. Specifically, a technique has been proposed wherein a rectangular electron beam is formed by electron irradiation unit and irradiated to a sample as a primary beam, and at least one of a secondary electron, a reflection electron and a back scattering electron (hereinafter referred to as a “secondary electron, etc.”) generated on the surface of the sample is projected as a secondary beam in an expanded form to an electron detector by a projection optical system, such that an image of the surface of the sample is obtained (e.g., Japanese patent laid open (kokai) 7(1995)-249393. In addition to the technique described in Japanese patent laid open (kokai) 7(1995)-249393, a method has also been proposed wherein a primary beam is deflected by a Wien filter which is an electromagnetic/magnetic superposed deflector to cause the primary beam to vertically enter the surface of a sample, and a secondary beam is also caused to travel straight within the same Wien filter to introduce the secondary beam into projection optics.
However, if, for example, an apparatus disclosed in Japanese patent laid open (kokai) 2002-222635 is used to irradiate a primary beam to a sample, a local difference is produced in the potential of the surface of the sample in accordance with the shape and material of the sample surface or of a layer in the vicinity of the surface. Even before the irradiation of the primary beam, a local difference is also produced in the potential of the surface in accordance with a condition in which the sample surface is charged.
For example, in the sample surface of an integrated circuit wafer in which a metal wiring line part and an inter-wiring-line insulator part coexist, a local potential gradient which is not parallel with the sample surface is produced in the vicinity of a boundary between the metal wiring line part and the insulator part, when the surface of the insulator part is positively charged or when the surface of the insulator part is negatively charged. When secondary electron beams released from a place in the metal wiring line part and a place in the insulator part in the vicinity of the boundary have their trajectories controlled by a secondary optical system and imaged in an MCP detector, the potential gradient brings about improper deflection effects, so that the secondary electron beams deviate from electron beam trajectories ideal for accurate projection, resulting in distorted electron beam trajectories. Consequently, the proper imaging of the secondary beam is prevented, which would be the cause of distortion and a decrease in contrast of a secondary electron beam detected image. This has caused a problem which leads to a decrease in the defect detection performance of the inspection apparatus.